JP2012178573A - Illumination system for euv lithography as well as first and second optical elements for use in illumination system of this type - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an illumination system for EUV lithography as well as a first optical element and a second optical element for use in an illumination system of this type.SOLUTION: A first optical element 7 is used to generate secondary light sources in an illumination system. A surface of the first optical element 7 impacted by EUV radiation is divided into a plurality of first facet elements 8 to 11. The latters are each associated with partial beams of the EUV radiation. A second optical element 20 at the position of the secondary light sources is impacted by EUV radiation over an impactable area via the first optical element 7, and an impactable surface is divided into a plurality of second facet elements 21 to 24. The latters are each associated with at least one of the first facet elements 8 to 11 impacting the respective second facet elements 21 to 24 to generate the secondary light sources.

Description

The invention relates to an illumination system for EUV lithography according to the preamble of claim 1.
The invention also relates to first and second optical elements for use in such an illumination system.

  A general purpose illumination system with corresponding first and second optical elements is known from US 6658084 B2. Other lighting systems are known from DE 10219514 Al and US 2007/0058274 Al. These published patents describe the generation of different illumination settings using displaceable field facet elements. With each of the different illumination system settings, the object surface is illuminated with a different illumination angle distribution. This known illumination system requires a very complex second optical element with a large number of pupil facets. This type of element is very expensive.

US6658084B2 DE10219514Al US2007 / 0058274Al US2003 / 0086524Al

  The object of the present invention is to develop an illumination system of the kind indicated at the beginning in such a way that it can be changed between different illumination settings even when a second optical element with fewer facet elements is used. It is to be.

This object is achieved according to the invention by an illumination system having the features described in the characterizing part of claim 1.
According to the present invention, it is not necessary to reproduce all the first facet elements in one and the same imaging area, but it can be configured as an assembly of individual partial fields that constitute the complete illumination field together. found. In doing this, the entire illuminated field is not illuminated through any of the partial fields. This basic approach allows the second facet element to be used in a more flexible way. These second facet elements can be illuminated by a plurality of first facet elements present at a certain spatial distance from each other. Partial beams of EUV radiation emanating from various first facet elements acting on one and the same second facet element are then imaged in various partial fields. This allows a partial beam of EUV radiation associated with a plurality of first facet elements to be imaged by one and the same second facet element. This flexibility allows a second optical element having a small number of second facet elements compared to the prior art to be used to generate various illumination settings, while the first facet element and the second facet element. The generation of illumination settings given a 1: 1 assignment of still a second optical element of this kind is still possible. Thus, different illumination settings can be generated without light loss and without exchanging optical components. While densely filling the second optical element, it is possible to produce a conventional setting, ie a uniform illumination of the second optical element. By dividing the illumination field into at least two partial fields, it is possible to preset the EUV intensity profile in the displacement direction of the object. For example, Gaussian, Lorentzian, trapezoidal, or other profiles can be set as defaults. By displacing the object and pre-setting the object surface at right angles to the partial field division of the illumination field, the object is illuminated over all partial fields so that each partial field achieves the role of illuminating a given object point. Can be guaranteed. This sequential illumination of object points across the partial field of view can be utilized, for example, to achieve desirable activation of a photosensitive wafer layer that is an example of an illuminated object surface.

The displaceable first facet element according to claim 2 provides the possibility of automatic change between different lighting settings.
The number of partial visual fields described in claim 3 is also the minimum number of partial visual fields required at the same time. The result is a compact illumination field. Two, three, or more first facet elements can be allocated to and act on the second facet elements.

The division of the illumination field according to claim 4 enables a relatively simple optical arrangement. The partial fields are adjacent to one another, particularly in the scanning direction, of the projection lighting installation of which the illumination system is a component. This ensures that the substrate to be illuminated, eg the wafer, scanned by the illumination field passes through at least two partial fields in succession.
The curved first facet element or partial field according to claim 5 reduces the requirements imposed on the optical arrangement.

The arrangement of facet elements according to claim 6 reduces the requirements imposed on the imaging, since large angles between the individual partial beams of EUV radiation can be avoided.
A second facet element that can be displaced by an actuator according to claim 7 increases the flexibility of the illumination system.
The lighting system according to claim 8 has a low loss.

The arrangement according to claim 9 allows a 1: 1 allocation of the first facet element to the second facet element.
The intersection between the partial fields of the illumination field according to claims 10 to 15 has been shown to be particularly advantageous for the practical realization of an illumination system for presetting the desired sequential illumination on the object surface. Yes.
The advantages of the illumination system according to claim 16 are the same as those of the illumination system according to claim 1.

Yet another object of the present invention is to provide first and second optical elements for an illumination system according to the present invention.
This object is achieved according to the invention by the optical element according to claims 17 and 18.
The advantages of these optical elements are the same as those already described above with reference to the illumination system according to the invention.
Embodiments of the present invention will be described below in more detail with reference to the drawings.

1 is a schematic diagram of a beam path in an illumination system for EUV microlithography. FIG. The components of the illumination system according to FIG. 1, more specifically, a first optical element divided into a plurality of facet elements for generating a secondary light source in the illumination system, the position of the generated secondary light source and on the object surface FIG. 5 is a schematic view of a second optical element divided into a plurality of second facet elements that are illuminated to provide a uniform conventional illumination setting in the illumination field of view. FIG. 3 is a view similar to that of FIG. 2 where the second facet element is illuminated to prepare a large diameter annular setting. FIG. 3 is a view similar to that of FIG. 2 in which the second facet element is illuminated to provide a uniform illumination setting with a small illumination angle compared to the illumination setting of FIG. FIG. 3 is a view similar to that of FIG. 2 where the second facet element is illuminated to prepare the lighting setting in an x-dipole manner. FIG. 3 is a view similar to that of FIG. 2 where the second facet element is illuminated to prepare the lighting setting in a y-dipole manner. FIG. 4 is a view similar to that of FIG. 3 of another embodiment having a curved first facet element. FIG. 3 is a view similar to that of FIG. 2 of another embodiment having a different magnification. FIG. 9 is a view similar to that of FIG. 3 of the embodiment according to FIG. 8.

FIG. 1 shows an illumination system 1 for illuminating a predetermined illumination field 2 of an object surface 3 with extreme ultraviolet (EUV) radiation 4.
A plasma light source is used as a light source for the EUV radiation 4. The wavelength of the EUV radiation is, for example, between 10 nm and 20 nm.
In FIGS. 1 and 2, an orthogonal coordinate system (x, y, z) is used, and is referred to by coordinates (x, y, z) below. In FIG. 1, the x direction extends perpendicular to the projection plane, the y direction extends to the right hand side, and the z direction extends downward.

  The EUV radiation emitted from the light source 5 is first collected by a concentrator 6 that reflects the EUV radiation as well as all subsequent steel guidance components. The EUV radiation 4 emitted from the light source 5 strikes a first optical element 7 also called a field scanning element. The first optical element 7 is used to generate a secondary light source in the illumination system 1. The reflective surface of the first optical element 7 irradiated by the EUV radiation 4 is divided into a plurality of first facet elements, of which four first facet elements 8 to 11 are exemplarily shown in FIG. These four first facet elements 8 to 11 are associated with partial beams 12 to 15 of EUV radiation 4. The first facet element is rectangular and its range is longer in the x direction than in the y direction. The aspect ratio (x: y) of the first surface elements 8 to 11 is 20: 1.

  Each of the first facet elements 8 to 11 can be tilted between various set positions with respect to an axis parallel to the x and y directions. For this purpose, each of the first facet elements 8 to 11 is connected to an associated actuator. In FIG. 1, as a representative example of these actuators, a first facet as indicated by a broken line at 17 to selectively tilt the facet element 11 with respect to one of two axes (x / y). An actuator 16 mechanically connected to element 11 is shown. Actuator 16 is connected to central control device 19 through control line 18. The control device 19 is connected to all other actuators associated with the first facet elements 8 to 11 and the first facet element not shown through corresponding control lines (not shown).

Examples of arrangements of first facet elements are shown in FIGS. 7 to 14 of US2003 / 0086524Al, which reference is made to all of them.
The second optical element 20, also called the pupil scanning element, is arranged in the position of the secondary light source generated by the first optical element 7, ie in the image plane relative to the light source 5. This second optical element 20 is impacted by the EUV radiation 4 through the first optical element 7. The impactable surface of the second optical element 20 is divided into a plurality of second facet elements, of which four facet elements 21 to 24 are exemplarily shown in FIG. Each of the second facet elements 21 to 24 is one of the first facet elements 8 to 11 such that a respective secondary light source occurs at a position of the second facet element 21 to 24 to which radiation has been applied respectively. Assigned to one. In the example according to FIG. 1, the second facet element 21 is assigned to the first facet element 8, the second facet element 23 is assigned to the first facet element 9, and the second facet element 22 is assigned to the first facet element. 10 and the second facet element 24 is assigned the first facet element 11.

  Similar to the first facet elements 8 to 11, the second facet elements 21 to 24 and the other facet elements not shown of the second optical element 20 are arranged by the actuator with respect to an axis parallel to the x and y directions. Can be tilted. FIG. 1 schematically shows, as an example, an actuator 25 associated with a second facet element 21 and mechanically connected to the second facet element 21 to tilt the second facet element 21 as indicated by the dashed line at 26. Is shown. The actuator 25 is in signal connection with the control device 19 through the control line 18.

The first facet element as well as the second facet element are reflective elements.
The second optical element 20 is part of an optical arrangement 27 that includes a plurality of optical components and forms an image of the first optical element 7 in a predetermined plane 30 by the object surface 3. The two reflective elements 28, 29 for EUV radiation belong to the optical arrangement 27, and the reflective element 28 downstream of the second optical element 20 reflects EUV radiation with a small incident angle, for example an incident angle of 30 °. The reflective element 29, which is arranged in the subsequent beam path of the EUV radiation 4, reflects EUV radiation with shallow incidence.

  FIG. 2 very schematically shows the allocation relationship between the first and second facet elements during imaging in the illumination field 2. In this respect, the projection plane of FIG. 2 is parallel to the xy plane, which is also true for the projection planes of FIGS. 3 to 9 below. For illustration purposes, the components shown in FIGS. 2-9 have been rotated into the xy plane. These components can actually be oriented in different ways. Components identical to those already described above with reference to FIG. 1 in FIGS. 2 to 9 have the same reference numerals and will not be described again in detail.

  FIG. 2 shows four facet elements 8 to 11 that represent all the first facet elements of the first optical element 7. The second facet elements 21 to 24 representing all the second facet elements of the second optical element 20 are arranged as follows in FIG. 2 for illustrative purposes. The second facet elements 21 and 24 are components of the inner ring comprising the second facet element. The second facet elements 22 and 23 are components of the outer ring of the second facet element. The generally circular second optical element 20 has a plurality of such concentrically arranged rings of second facet elements. The second facet elements can be arranged in a uniformly distributed x / y raster manner. FIG. 15 of US2003 / 0086524Al provides this example.

  The allocation of the first facet elements 8 to 11 to the second facet elements 21 to 24 is such that it produces a uniform conventional lighting setting. All second facet elements of the second optical element 20 combined with other second facet elements not shown, i.e. not only the illustrated second facet elements 21 to 24, but also all other second facet elements of the associated raster. Two facet elements are also illuminated by the respective first facet element. That is, the second optical element 20 is illuminated uniformly.

  The first facet elements 8 and 10 are configured and oriented in such a way that these elements are imaged in the lower partial field 31 of the illumination field 2 by the optical arrangement 27 in the arrangement of FIG. The The first facet elements 9 and 11 are configured and oriented in such a way that these elements are imaged by the optical arrangement 27 in the upper partial field 32 of the illumination field 2. The two partial fields 31, 32 have the same surface area. The partial fields 31, 32 have the same aspect ratio as the first facet elements 8-11. The two partial fields 31 and 32 are slightly bowed due to the imaging characteristics of the optical arrangement 27. The two partial fields 31 and 32 constitute a complete illumination field 2. In the ideal example shown in FIG. 2, the two partial fields 31, 32 are directly adjacent to each other without overlapping. In practice, the two partial fields 31 and 32 overlap each other in such a way that the intersection of the two partial fields 31 and 32, that is, the overlapping region is always smaller than the area of each partial field 31 and 32.

In the embodiment according to FIG. 2, the first facet elements 8 to 11 are imaged in the image plane 30 with a negative magnification.
As a result of the division of the illumination field 2 into two partial fields 31, 32, the illumination occurs at a selected illumination angle among all illumination angles present in the illumination setting according to FIG. 2 in each partial field. A portion of every second facet element is illuminated in each of the partial fields 31, 32. Only by the superposition of both partial fields 31, 32, the object surface 3 is illuminated at all illumination angles of the illumination setting. This superposition is performed by displacing the object surface 3 in the y direction. This displacement can be carried out continuously or stepwise, in which case the step length should not be longer than the range of y of the partial field. In this manner, each point on the object surface 3 that passes through both partial fields 31, 32 accumulates the exposure effect of the EUV radiation emitted thereto, so that after this pass the illumination is set to the illumination setting. It was implemented from all possible illumination angles.

  FIG. 3 shows another illumination setting possible with the arrangement of FIG. This other illumination setting is known as a large annular setting. This large annular setting starts from the situation according to FIG. 2, in which the first facet element 8 is tilted with respect to its longitudinal axis parallel to the x direction and the second facet element 11 is parallel to the y direction. It is set by inclining with respect to its longitudinal axis. As a result of these tilting movements, here the first facet element 8 acts on the second facet element 23 and the first facet element 11 acts on the second facet element 22. Therefore, at this time, the second facet element 22 is associated with two first facet elements, more specifically, the first facet elements 10 and 11. Accordingly, the second facet element 23 is associated with the first facet elements 8 and 9. The second facet elements 22, 23 are in the lighting setting according to FIG. 3 so that they are therefore two different adjacent first facet elements, more specifically on the one hand the first facet elements 10 and 11 and on the other hand. Arranged in such a way as to be acted upon by one facet element 8, 9 respectively. The second facet elements 21, 24 are not acted on by the first optical element 7.

In FIG. 3, the lower partial field 31 is illuminated by radiation from the first facet elements 8 and 10, similar to the setting according to FIG. The upper partial field 32 is illuminated by radiation from the first facet elements 9 and 11.
When changing the illumination settings between those shown in FIG. 2 and those shown in FIG. 3, the second facet elements 22, 23 need not be displaced.
In the annular setting according to FIG. 3, the illumination angle varies between a minimum illumination angle different from zero and a maximum illumination angle.

FIG. 4 shows another illumination setting that can be generated using the arrangement according to FIGS. This setting is known as a small conventional setting with a maximum illumination angle that is smaller than the minimum illumination angle of the annular setting according to FIG.
Compared to the setting of FIG. 2, in FIG. 4, the two first facet elements 9 and 10 are inclined in the x and y directions, respectively. Here, the first facet element 9 acts on the second facet element 21 together with the first facet element 8. The first facet element 10 acts on the second facet element 24 together with the first facet element 11. The first optical element 7 does not act on the second facet elements 22 and 23.
Similar to the setting according to FIG. 2, in FIG. 4, the lower partial field 31 is illuminated by radiation from the first facet elements 8 and 10. The upper partial field 32 is illuminated by radiation from the first facet elements 9 and 11.
When changing between the lighting settings according to FIGS. 2 and 4, the second facet elements 21, 24 need not be displaced.

  FIG. 5 shows another illumination setting that can be generated using the arrangement according to FIGS. This setting is an illumination setting in a method known as an x dipole. In this case, the illumination corresponding to the conventional setting according to FIG. 2 occurs in the xz plane over various illumination angles. At right angles to the xz plane, i.e., in the yz plane, illumination occurs in a region of small illumination angles that can increase outward.

In the setting according to FIG. 5, the beam path starting from the first facet elements 10, 11 corresponds to the beam path set according to FIG. The radiation emanating from the first facet elements 8 and 9 cooperates to illuminate the second facet element 24, and the radiation emanating from the first facet element 8 is imaged in the lower partial field 31, and the first facet element The radiation emanating from 9 is imaged in the upper partial field 32.
During the transition between the illumination setting according to FIG. 2 and the illumination setting according to FIG. 5, in order to ensure that the radiation emanating from the first facet elements 8 and 9 is actually correctly imaged in the illumination field 2, The second facet element 24 needs to be tilted.

  FIG. 6 shows another illumination setting that can be generated in the arrangement according to FIGS. This setting is an illumination setting in a method known as the y-dipole mode. According to what has been implemented with respect to the setting of FIG. 5, in the setting of FIG. 6, the illumination angle in the illumination field has an angular distribution similar to the conventional setting according to FIG. 2 in the yz plane and in the yz plane according to FIG. The illumination angle distribution corresponding to is distributed in such a way as to exist in the xz plane.

Compared with the setting of FIG. 2, in order to adjust the setting according to FIG. 6 so that the radiation emanating from the first facet element 10, 11 is correctly imaged in the illumination field 2, the first facet element 8, 10, and It is necessary to tilt the second facet element 21 as well as 11.
In the setting according to FIG. 6, the first facet elements 8, 9 cooperate to illuminate the second facet element 23, and the first facet elements 10, 11 cooperate to illuminate the second facet element 21.

FIG. 7 shows another embodiment of a lighting system similar to that of FIGS. 1 and 2, adjusted to a lighting setting similar to that of FIG. Components corresponding to those already described above with reference to FIGS. 1 to 6 have the same reference numerals and will not be described again in detail. In contrast to the rectangular first facet elements of the embodiment according to FIGS. 1 and 2, the first optical element 7 of the arrangement according to FIG. 7 has first facet elements 8 to 11 which are slightly arcuately curved.
The curved first facet elements 8 to 11 are imaged in the curved partial fields 31, 32 by the optical arrangement 27.

8 and 9 show another embodiment of the lighting system 1. Components corresponding to those already described above with reference to FIGS. 1 to 7 have the same reference numerals and will not be described again in detail.
In contrast to the embodiment according to FIGS. 1 to 7, the optical arrangement 27 of the embodiment according to FIGS. 8 and 9 to which other reflective elements such as elements 28 and 29 (not shown) as well as the second optical element 20 belong. Has a positive magnification. In the embodiment according to FIGS. 8 and 9, the first facet elements 9 and 11 are now imaged in the lower partial field 31 of the illumination field 2. The first facet elements 8 and 10 are imaged in the upper partial field 32.

FIG. 8 shows a conventional setting corresponding to that of FIG. For guidance of partial beams 12-15, the first facet element 8 is associated with a second facet element 23, the first facet element 9 is associated with a second facet element 21, and the first facet element 10 is Associated with the second facet element 22, the first facet element 11 is associated with the second facet element 24.
FIG. 9 shows another illumination system generated by tilting the first facet elements 9 and 11 so that in the arrangement according to FIG. 8 a large annular setting like the setting of FIG. 3 is generated. . For the second facet element 23, two first facet elements 8 and 9 act in cooperation. For the second facet element 22, the two first facet elements 10 and 11 act in cooperation.

The illumination system 1 is a projection illumination facility for microlithography where an object having an object surface, for example a mask or a reticle, is imaged on a wafer to produce an integrated component, for example a microprocessor or a memory chip. It is a part.
The first optical element 7 can be configured such that only the specific first facet element can be tilted by the actuator while the other first facet elements remain stationary. The second optical element 20 can also be equipped with a tiltable second facet element and a stationary second facet element accordingly. It is also possible to equip a second optical element 20 which generally has a stationary second facet element, in other words without providing a tilt option.

The number of first facet elements of the first optical element 7 is equal to the number of second facet elements of the second optical element 20. Alternatively, a second optical element 20 can be provided in which the number of facet elements is greater or smaller than the number of first facet elements of the first optical element.
In the embodiment described above, a maximum of two first facet elements 8 to 11 are associated with the second facet elements 21 to 24. In each case, it is also possible to associate more than two first facet elements with second facet elements. The minimum number of partial fields constituting the illumination field increases accordingly.
In principle, it is also possible to configure at least individual components of the lighting system as transmissive components.

2 Illumination field 7 First optical element 8, 9, 10, 11 First facet element 20 Second optical element 21, 22, 23, 24 Second facet element 31, 32 Partial field

Claims (18)

a) aa) impacted by EUV radiation (4),
ab) the impacted surface of the optical element is divided into a plurality of first facet elements (8 to 11), each assigned to a partial beam (12 to 15) of the EUV radiation (4);
A first optical element (7) for generating a secondary light source in the illumination system (1);
b) ba) impacted by EUV radiation (4) through said first optical element (7), bb) its impactable surface being divided into a plurality of second facet elements (21 to 24), each of which Assigned to at least one of the first facet elements (8 to 11) acting on the respective second facet elements (21 to 24) to generate the secondary light source;
bc) at least part of an optical arrangement (27) for imaging the first optical element (8 to 11) in a plane (30) predetermined by the object surface (3).
Having a second optical element (20) in the position of the secondary light source generated by the first optical element (7);
An illumination system (1) for EUV lithography for illuminating a predetermined illumination field (2) of an object surface (3) with EUV radiation (4),
c) At least two of the first facet elements (8 to 11) are one of at least two partial fields (31, 32) of the illumination field (2) that they constitute the entire illumination field (2) and If an intersection between the partial fields (31, 32) is imaged on the same by an optical arrangement (27) and there is such an intersection, the partial fields (31, 32) that contribute to the intersection 32) configured and oriented to be always smaller than each of
A lighting system (1) characterized by the above. For selective illumination of a given illumination field (2) of the object surface (3) with EUV radiation (4) in a setting selected from various illumination settings that can be predetermined.
bc) At least selected ones of the first facet elements (8 to 11) are set in various ways by the actuator (16) associated with the selected first facet element (8 to 11) in each case. Can move between positions,
bd) At each set position of the movable first facet element (8 to 11), the partial beam (12 to 15) associated with it in each case is deflected by the movable first facet element (8 to 11). To generate one of the predetermined lighting settings,
e) At least one of the second facet elements (21 to 24) can be acted on by at least two different first facet elements (8 to 11) in at least one of the predetermined lighting settings. Positioned in such a way,
The illumination system according to claim 1.   System configuration such that the number of partial fields of view (31, 32) corresponds to the maximum number of first facet elements (8 to 11) that can act on the same second facet element (12 to 24) The illumination system according to claim 1 or 2.   4. The illumination field is divided into at least two adjacent partial fields (31, 32), in particular in the form of a partial field zone having the same surface area. Lighting system.   5. Illumination system according to claim 4, characterized in that the first facet element (8 to 11) and / or the partial field (31, 32) are curved.   At least one of the second facet elements (21 to 24) is arranged in such a way that exactly two adjacent first facet elements (8 to 11) can act on it. The illumination system according to any one of claims 1 to 5.   At least one of the second facet elements (21 to 24) is in various set positions using an actuator (25) associated in each case with the selected second facet element (21 to 24). The illumination system according to any one of claims 2 to 6, wherein the illumination system can be displaced between the two.   8. Illumination system according to any one of claims 1 to 7, characterized in that the first and / or second facet elements (8 to 11, 21 to 24) are configured as reflective elements.   9. The number of the first facet elements (8 to 11) is the same as the number of the second facet elements (21 to 24). Lighting system.   10. The crossing between the partial fields (31, 32) is less than 95% of the smallest partial field (31, 32) contributing to the intersection. The lighting system according to any one of claims.   10. The crossing between the partial fields (31, 32) is less than 90% of the smallest partial field (31, 32) contributing to the intersection. The lighting system according to any one of claims.   10. The crossing between the partial fields (31, 32) is less than 80% of the smallest partial field (31, 32) that contributes to the intersections. The lighting system according to any one of claims.   10. The crossing between the partial fields (31, 32) is less than 60% of the smallest partial field (31, 32) that contributes to the intersections. The lighting system according to any one of claims.   10. The crossing between the partial fields (31, 32) is less than 40% of the smallest partial field (31, 32) contributing to the intersection. The lighting system according to any one of claims.   10. The crossing between the partial fields (31, 32) is less than 20% of the smallest partial field (31, 32) that contributes to the intersections. The lighting system according to any one of claims. a) aa) impacted by EUV radiation (4),
ab) the impacted surface of the optical element is divided into a plurality of first facet elements (8 to 11), each assigned to a partial beam (12 to 15) of the EUV radiation (4);
A first optical element (7) for generating a secondary light source in the illumination system (1);
b) ba) impacted by EUV radiation (4) through said first optical element (7), bb) its impactable surface being divided into a plurality of second facet elements (21 to 24), each of which Assigned to at least one of the first facet elements (8 to 11) acting on the respective second facet elements (21 to 24) to generate the secondary light source, and bc) preliminarily by the object surface (3) At least part of an optical arrangement (27) for imaging the first optical element (8 to 11) in a defined plane (30);
Having a second optical element (20) in the position of the secondary light source generated by the first optical element (7);
An illumination system (1) for EUV lithography for illuminating a predetermined illumination field (2) of an object surface (3) with EUV radiation (4),
At least two of the first facet elements (8 to 11) are imaged in the illumination field (2) through one and the same second facet element (21 to 24);
A lighting system (1) characterized by the above.   A first optical element (7) for use in an illumination system (1) according to any one of the preceding claims.   A second optical element (20) for use in an illumination system (1) according to any one of the preceding claims.

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